Green’s Dictionary of Slang

1. (UK und.) the Assizes.

1935

Thieves Slang ms list from District Police Training Centre, Ryton-on-Dunsmore, Warwicks 4: Fully: The big fully is the Assizes [ibid.] 6: Little Fully: Sessions.

2. (US gang) an automatic weapon, e.g. an Uzi, Glock or Tech Nine, as used in gang wars [SE fully automatic].

1993		K. Scott Monster (1994) 382: Other parts of South Central are still conducting their ‘ralks’ with fullies, body armor and pagers.
1995		Mack 10 ‘Mack 10’s The Name’ 🎵 Let Me Ride on these niggaz, check em nine double-m fully tech em / Straight up gun play one way, rat-a-tat-tat em / Buck red hot ones at em, aim at em, flame at pop-um.